Growth Hormone Releasing Activity Research Articles

Influence of insulin injected into the lateral ventricle on pituitary growth-hormone release in the rat.

SUMMARY Injections of insulin (0·2 or 0·01 i.u./20 μl) into the lateral ventricle of the rat brain, while not changing blood glucose levels or altering the pituitary content of growth hormone (GH), blocked the release of GH from the pituitary and the decrease of growth-hormone releasing activity (GHRF) of stalk median eminence (SME) extracts in the presence of the hypoglycaemic effect on insulin (2 i.u./kg) given intraperitoneally. Intraventricular administration of insulin also impaired the GH release elicited by cold exposure (4 °C, 1 h) but not the release induced by electric shock. The possibility that insulin injected into the brain acts on glucose-sensitive GH-regulating structures is suggested.

Thyrotropin and growth hormone releasing activity in hypophysial portal blood.

Studies of TSH and GH releasing activities in plasma from pituitary stalk blood have been conducted. TSH and GH released from anterior pituitary halves incubated in vitro with either portal or peripheral plasma were measured by means of specific radioimmunoassays. Relative to peripheral plasma, portal plasma resulted in 161 % increase in TSH secretion and 149 % increment in GH secretion. Electrical stimulation of the anterior hypothalamus further augmented TSH release to 201 %, but no further GH release was observed after electrode stimulation. Prior treatment with triiodothyronine did not abolish the influence of electrical stimulation upon TSH releasing activity. Both TSH and GH were also identified in portal plasma. It was estimated that these tropic hormones, presumed to originate from pars tuberalis, could contribute as much as 5 % of circulating TSH and GH in the periphery of intact rats.(Endocrinology 87: 807, 1970)

Norepinephrine and dopamine injection into lateral brain ventricle of the rat and growth hormone-releasing activity in the hypothalamus and plasma.

The effect of norepinephrine (NE) or dopamine (DA) on the growth hormonereleasing (GRF) activity in the hypothalamus and plasma of intact or hypophysectomized rats was studied by administering the catecholamines into the lateral ventricle of the brain. Growth hormone-releasing activity was evaluated by the depletion of pituitary growth hormone produced by intracarotid injection of hypothalamic extracts or plasma. NE and DA at doses known to be effective in depleting GH from the pituitary (0.5 μg) induced in intact and hypophysectomized rats disappearance of GRF activity from the hypothalamus and its appearance in plasma from hypophysectomized but not from intact rats. Unlike adrenergic compounds, serotonin (0.5 μg) was inactive. In intact rats NE given intraventricularly induced a depletion of pituitary GH activity at doses from 0.05 to 0.0025 μg. Dopamine at a dose of 0.005 μg was inactive. These results, while pointing to a hypothalamic site of action for the GH-releasing effect of catecholamines, tend ...

Variability of response in the bioassay for a hypothalamic somatotrophin releasing factor based on rat pituitary growth hormone content.

The bioassay based on “pituitary depletion of growth hormone content” in the rat as described by Pecile et al. (Endocrinology 77: 241, 1965) has been used to assess “growth hormone releasing activity” in crude extracts of ovine, porcine, bovine hypothalamus and purified fractions of ovine hypothalamus extracts following gel filtration on Sephadex G-25. In all experiments, control pituitary glands were assayed for growth hormone (tibia test) at 2 dose levels; experimental pituitaries were assayed for growth hormone at 2 dose levels, or at one single dose corresponding by weight of pituitary tissue to the highest dose of the control or bracketed between the 2 doses of the control glands. The results of all experiments were studied by analysis of variance, followed by the multiple comparison test of Dunnett, the multiple range test of Duncan to assess significant differences between experimental and control groups and bioassays (3-point or 4-point). With these strict mathematical criteria for validity, contr...

Growth hormone releasing activity in the hypothalamus of rats subjected to prolonged heat stress.

SummaryThe experiment investigated the effect of a high ambient temperature (35.6°) of varying duration on the hypothalamic content of growth hormone releasing activity (GHRA). These experiments consisted of five treatment groups: one group of normals at 24°, one sham-treated group receiving only diluent in which hypothalami were extracted, and three groups, each heatexposed for 1, 24, or 168 hr, respectively. The GHRA was measured by in vivo depletion of pituitary growth hormone (GH) content in 30-day-old rats. Pituitaries of the recipient rats were assayed by the “tibia test” method for GH content. The standard assay was based on three doses of bovine growth hormone (NIH-GH-B12) with a threefold difference between consecutive levels. Growth hormone was evaluated by two parameters: (a) epiphyseal cartilage width, and (b) GH content of the unknown estimated from the response in terms of the reference standard. An exposure to heat for 1 or 24 hr resulted in an enhanced hypothalamic GHRA with a concomitant ...

Pituitary growth hormone content and hypothalamic growth hormone releasing activity in neonatal rats after stress.

A remarkable growth hormone releasing (GRF) activity was found in hypothalamic stalk median eminence (SME) extracts of neonatal rats. The application of electric shock to rats of 1, 5, and 10 days of age induced a clear-cut decrease in pituitary growth hormone content. In the shocked animals GRF activity in the hypothalamic SME extracts was significantly reduced. These results indicate that in the very early stages of development all mechanism(s) which bring about growth hormone release are available, and that a response to stressful stimuli may be expected in infant rats as well as in adult rats.

Growth hormone releasing activity in rhesus monkeys of crude ovine stalk median eminence extracts.

Intravenous injections of crude extract of ovine stalk median eminence (SME) produced significant increases in plasma growth hormone (GH) in unanesthetized rhesus monkeys. The effective dose was 15–30 mg/kg. The plasma GH response was specific, i.e., due to substance(s) in SME, because injections of saline, trypsin-treated SME, crude ovine cerebral cortical extract or thioglycollate-treated argin-ine-8-vasopressin (thio-AVP) failed to produce significant responses. Since crude SME had pressor activity, it was possible that all the GH releasing activity of SME was due to the vaso-pressin in the extract. This possibility was rejected when it was shown that thioglycollate abolished pressor activity of SME and reduced, but did not abolish, GH releasing activity. Identical thioglycollate treatment of AVP abolished both pressor activity and its GH releasing activity. All GH releasing activity of SME was abolished by tryptic digestion. This strongly suggests, but does not prove, that all the GH releasing substances in SME are peptides. The relationship between the specific, thioglycollate-stable GH releasing activity of ovine SME described in this paper and the specific ovine GH-RF which depletes rat pituitary GH activity remains to be established. (Endocrinology83: 25, 1968)

Growth hormone-releasing activity in the hypothalamus of animals of different species

Hypothalamic extracts from the dog, rabbit, mouse, kitten, pigeon, and frog were found to decrease the growth hormone (GH) content of rat pituitary glands. Comparable cerebral cortical extracts were completely inactive in this test. These results broaden previous observations on the existence of a GH-releasing factor (GRF) in the hypothalami of mammals and show the presence of GRF activity in birds and amphibians.

Growth Hormone-Releasing Activity in the Hypothalamus and Plasma of Rats Subjected to Stress.

SummaryExperiments were performed in the rat to determine whether the increased secretion of growth hormone (GH) during stress involves augmentation of synthesis and/or release of hypothalamlc GH-releasing factor (GRF). Two different stimuli were used as stress: injection of formalin, which was previously shown to be ineffective in inducing GH release; and cold exposure, which evoked depletion of pituitary GH. Exposure of rats to cold (4°C) for 1 hr resulted in a significant depletion of pituitary GH, which was accompanied by disappearance of hypothalamic GRF and appearance of GRF activity in plasma. Cold exposure for 5 minutes was ineffective. Injection of 10% formalin did not induce pituitary GH depletion, or affect hypothalamic and plasma GRF activity. These results indicate that some stressful stimuli, such as cold exposure, capable of releasing GH, induce this effect via the hypothalamus; other stresses, like formalin injection, which do not release GH, exert little effect on the GH-release mechanism...

Growth hormone-releasing activity in plasma of normal and hypophysectomized rats.

Growth hormone (GH)-releasing activity in plasma of normal or hypophysectomized male rats was investigated by the method of in vivo depletion of growth hormone in rat pituitaries. Plasma from rats hypophysectomized about 3 months previously depleted pituitary growth hormone when injected into the carotid artery of 40-day-old recipient rats. This activity was absent in plasma of rats hypophysectomized for only a week and from plasma of normal rats of the same age as the hypophysectomized rats. The GH-releasing activity of plasma from long-term hypophysectomized rats appeared to be of neural origin, since it was not present in aortic plasma 10 min after elimination of the cranial circulation. (Endocrinology 80: 77, 1967)

Growth hormone-releasing activity in the hypothalamus of primates.

Growth hormone (GH)-releasing activity of simian and human hypothalamus was investigated by the method of in vivo depletion of growth hormone content of rat pituitaries. The extracts of the stalk-median eminence (SME) region prepared from 6- to 8-month-old rhesus monkeys and from a 3-year-old child were injected into the carotid artery of 30-day-old recipient rats. The pituitaries of the recipient animals were assayed for GH content by the “tibia test” method. Rhesus monkey SME extracts induced in the recipient rats a depletion of growth hormone pituitary content of about 70 %. Human SME extract caused a depletion of GH content of about 50 %. Comparable cerebral cortex extracts of simian and human origin had no effect on pituitary GH content. These findings indicate that a growth hormone-releasing activity is present in the hypothalamus of primates. (Endocrinology 79: 448, 1966)

Maintenance of growth hormone releasing activity in the hypothalamus of long-term hypophysectomized rats.

In animali ipofisectomizzati da un anno l'attività somatotropo liberatrice degli estratti di eminenza mediana dell'ipotalamo si è dimostrata simile a quella di analoghi estratti ottenuti da animali normali della stessa età.

Growth hormone-releasing activity of crude ovine hypothalamic extracts.

Growth hormone-releasing activity of crude ovine hypothalamic extracts.

Substances present at the hypothalamic level and growth hormone releasing activity.

Substances present at the hypothalamic level and growth hormone releasing activity.

Growth hormone-releasing activity of hypothalamic extracts at different ages.

An investigation of the growth hormone-releasing activity of hypothalamic extracts from young growing animals and from animals which had reached growth stasis was undertaken to determine if a different growth hormone-releasing activity might be present in hypothalamic extracts with advancing age. For this purpose, hypothalamic extracts from 30-day-old rats and 2-year-old rats (5 mg/100 g body wt) of rat stalk-median eminence region were tested in vivo using intracarotid injections into 30-day-old recipient female rats. The pituitaries of the recipient animals were assayed for growth hormone content by the “tibia test” method. Hypothalamic extracts from 30-day-old rats induced an almost complete depletion of pituitary growth hormone content. This depletion effect of pituitary growth hormone content was not duplicated by hypothalamic extracts taken from 2-year-old animals and injected in equivalent amounts. These results strongly suggest the presence, in young animals, of a growth hormone-releasing factor (...